DNA rearrangements in human follicular lymphoma can involve the 5' or the 3' region of the bcl-2 gene.

Abstract

In most human follicular lymphomas, the chromosome translocation t(14;18) occurs within two breakpoint clustering regions on chromosome 18, the major one at the 3' untranslated region of the bc1-2 gene and the minor one at 3' of the gene. Analysis of a panel of follicular lymphoma DNAs using probes for the first exon of the bc1-2 gene indicates that DNA rearrangements may also occur 5' to the involved bcl-2 gene. In this case the IgH locus and the bc1-2 gene are found in the order 3' C.y Sy/1, JH 5'::5' bcl-2 3' (where C = constant, S = switch, and JH = joining segment of the heavy chain locus), suggesting that an inversion also occurred during the translocation process. The coding regions of the bc1-2 gene, however, are left intact in all cases of follicular lymphoma studied to date.More than 80% of human follicular lymphomas carry a t(14;18)(q32;q21) chromosome translocation (1, 2). This translocation directly involves the immunoglobulin heavy chain (IgH) locus and the bc1-2 (B-cell lymphoma/leukemia 2) gene (3,4). By comparing the structures of bc1-2 cDNA clones and genomic DNA clones, we have shown that the human bc1-2 gene consists of at least two exons separated by an intron of >50 kilobases (kb) of DNA (5). The first exon is transcribed into a 3.5-kb mRNA (5) (also see Fig. 1). This exon contains a splicing donor signal so that bc1-2 mRNA is spliced to the second exon to produce a 5.5-kb and an 8.5-kb mRNA (5) (also see Fig. 1). The 5.5-kb and 3.5-kb mRNA code for the bcl-2 a and , protein, respectively, which are identical except for the carboxyl-terminal portion (5). We have shown that '60% of the breakpoints of the t(14;18) translocation on chromosome 18 are tightly clustered in the 3' noncoding region of the bc1-2 gene (3-5) and -10% are clustered at a region 3' to the bc1-2 gene (3, 4) (also see Fig. 1). We have also shown that the association of the bc1-2 gene with the heavy chain locus results in high levels of bc1-2 expression (3). In all cases we have analyzed previously, the immunoglobulin heavy chain (IgH) locus, including the IgH enhancer, is 3' to the involved bcl-2 open reading frames (3-5), suggesting that the IgH locus is responsible for the bc1-2 activation in the follicular lymphomas. MATERIALS AND METHODSGel Electrophoresis and Southern Transfer. High molecular weight DNA was digested with restriction endonucleases and 5-,ug samples were fractionated on 0.7% agarose gels and transferred to nitrocellulose filters essentially as described by Southern (6).Construction of Genome 2 DNA Library. DNA extracted from the follicular lymphoma FL989 was partially digested with restriction enzyme Sau3AI and DNA fragments between 15 and 23 kb were collected. DNA inserts were ligated with XEMBL3A phage vector DNA cut with BamHI and packaged in vitro (7,8). Two recombinant phage clones, containing a fragment corresponding in size to the rearranged bcl-2 first exon sequences, were obtained by screening the library with the bcl-2 first exon probe pB16 (5).DNA Sequencing. Nucleotide sequences wer...

t(14;18), a journey to eternity

“…In one case, the breakpoint was mapped about 10 kb upstream of the bcl-2 locus within another transcriptionally active locus which is called follicular variant translocation gene (fvt-1). 13 The IgH J H 6 region was coupled to bcl-2 in one case, 14 but in most cases the kappa or lambda immunoglobulin light chain genes (IgL) are juxtaposed to bcl-2 in a head-to-head orientation, resulting in the t(2;18)(p11;q21) or the t(18;22) (q21;q11). 2,15,16 Based upon molecular analysis using Southern blot, the t(2;18) and t(18;22) have been associated only recently with B cell chronic lymphocytic leukemia (B-CLL), and seem to occur in about 5% of cases (Table 2).…”

Evaluation of bcl-2 protein expression and 14;18 translocation as prognostic markers in follicular lymphoma

“…Southern blotting and polymerase chain reaction Southern blotting for detection of rearrangement in the major, the minor and the 5' breakpoint regions of the bcl-2 gene was performed as described (Pezzella et al, 1990a;Tsujimoto et al, 1987).…”

Molecular features of a new human lymphoma cell line carrying both BCL2 and BCL6 gene rearrangements

“…DNA probes used in this study were as follows: pB16 probe (Tsujimito et al, 1987) was a cDNA fragment corresponding to the second exon of BCL2 and was used to detect rearrangements within the 5'-BCL2; probe b (Tsujimoto et al, 1985) and pFL-2 (Cleary et al, 1986) recognized the MBR and the mcr of BCL2, respectively; F370 probe was within the ®rst intron of BCL6; M55 probe (Kerckaert et al, 1993) was a cDNA clone for the BCL6; and Jk probe (Hieter et al, 1982) corresponded to the J region of IGk.…”